US1074625A - Carbureter. - Google Patents

Description

E. T. JOHNSON, W. H. GLASER & H. R. LLOYD.

GARBURETBR.

APPLICATION FILED MAR. 30, 1912.

1,974,625, V Patented Oct. 7,1913.

3 SHEETS-SHEET 2.

Patented 0011.7,1913.

3 SHEETS-SHEET 3 GARBURETER.

APPLICATION FILED MAR. 30, 1912.

E. T. JOHNSON, W. H. GLASER & H. R. LLOYD.

v f L pr m H 6 z 9 m m M A 0 0 1 PM. WW

To all whom it may concern:

UNITED STATES PATENT curios.

ERIC TOWNSEND JOHNSON, F TIMPERLEY, AND WILLIAM HENRY GLASER AND HAROLD BHYS LLOYD, OF CHEADLE HULME, ENGLAND.

GARBURETER.

Specification of Letters Patent.

Patented Get. 7, 1913.

Application filed March 30, 1912. Serial No. 687,298.

Be it known that we, E1210 TowNsnNn JOHNSON, a resident of Timperley, and WIL- LIAM HENRY GLASER and HAROLD RHYs LLOYD, residents of Cheadle Hulme, in the county of Chester, England, all subjects of the King of Great Britain, have invented new and useful Improvements in Carbureting Apparatus, of which the following is a specification.

This invention relates to carburetors, principally for use with internal combustion engines such as are employed for instance on automobiles.

The principal object of the invention is to provide a carbureter which will give automatically a constant or approximately constant mixture of air and spirit throughout a wide range of speeds of flow of the air, 11. 6. throughout a wide range of working speeds of the engine. .It may be desirable to have a relatively rich mixture, 27. 6. one containing an excessive amount of spirit in proportion to the air at low speeds, while at higher speeds the mixture is of normal strength and is practically constant in strength. Such a result is readily obtainable in accordance with this invention in a carbureter which operates automatically Without the use of any valves or like moving parts except such as are needed to maintain an approximately constant amount of fuel in the feed chamber.. This object is attained by the use of a contracting pipe of a kind sometimes called a Venturi pipe, through which the charges are drawn in by the engine, and in which the mixing or carbureting takes place. The. suggestion has been made already to use such a Venturi pipe in a carburetor with a spirit inlet at the narrowest section communicating with a float feed chamber, the spirit being forced out by the varying pressure of the air on the surface of the spirit in the said chamber; this pressure was to be produced by having the float chamber closed except for a passage at its upper end communicating with apertures in the Venturi pipe at or near-its largest section. It was then supthis formula :-a and p, are the area and posed that the pressure difference between .the air pressure apertures and the spirit in let aperture would be proportional to the square of the quantity or speed of the air flowing through the ipe for any positions of the apertures, an that the amount of spirit forced through the jet would beproportional to the square root of the pressure lead, so that the feed of spirit would be directly proportional to the amount of air flowing through the pipe. A Venturi pipe was to be used having its sectional area at the narrowest part about one eighth of the sectional area at the place where the air pressure openings are made. The above is mentioned in order to distinguish clearly from it the differences in theory and con- .struction on which the present invention is based. The said carbureter would have operated correctly only if-air were an incompressible fluid, z. e. one which did not expand or contract with pressure changes, and if the air could be assumed to be at rest at the inlet of the pipe. These assumptions cannot be made, and in order to design a satisfactory carburetor using a Venturi-pipe as above, it is necessary to take into account the expansion of the air under reduction of pressure, and the drop in pressure of the air at the inlet of the pipe. Itis also essential to insure substantially stream-line flow of the air through the pipe so that the rate of flow and the pressures may vary as required, and for this purpose a pipe must be used whose contraction of sectional area from the inlet is such that the narrowest sectional area is not less than about 60 per cent. of the inlet area, while the pipe contracts gradually and approximately uniformly from the inlet to the neck.

In designing the carbureter use is made of the following formula which correctly represents the relation betwen the area and pressure in a gas flowing through a ipe of gradually varying sectional area, neg ecting only slight errors such as that due to friction, which is very small in a short pipe such as is used according to the present invention'. The formula is g aar-taps F' "va a pressure respectively of the air at the inlet opening of the pipe, and a and 20, are the area and pressure at another point in the pipe. 9 is the acceleration due to gravity, as usual. ris the ratio for air of the specific heat at constant pressure to the specific heat at constant volume. W represents the rate of flow of the air in units of mass per unit of time. V represents the volume of unit mass of air at the pressure 12,. The method -of using this formula and lts application to the design of a particular carbureter will now be described with reference to the accompanying drawings, wherein Flgure 1 is a diagram showing curves obtained from the above formula. Fig. 2 is a section of a carbureter according to the invention, having its pipe vertical. Fig. 3 is a view partl in section, of the same carbureter seen rom the side. Fig. 4 is a plan View thereof. Figs. 5, 6 and 7 are detail views showing sections of three different forms of horizontally arranged carburet'ers.

Fig. 8 is an enlarged sectional view of a supply chamber for the spirit orliquid fuel, and Fig. 9 is a partial face'view of a diaphragm used in said chamber.

The procedure in designing a carbureter according to the invention is as follows: The quantity W is estimated for the maximum speed of flow, that is to say, the speed of flow when working with an engine at maximum speed and with the throttle valve fully open. From this anarea a, is chosen for the pipe large enough to insure stream line flow of the air. A pressure p, is assumed (less than atmospheric pressure) and also 'a pressure p not less than 70 per cent. of p, in order that stream line flow may be insured. The assumed pressure 12, may be estimated by experiment or calculation, but it is not necessary to determine it very accurately as the error due" to choosing p, slightly too large or too small is inappre ciable. The value of a, for the throat or neck of the pipe is next determined from the formula above, and also various intermediate values of p, for intermediate values of a. After this the calculations are repeated taking W for two thirds the maximum load and again for one third the maximum load, assuming in each case su'itable values for p, which will be nearer to atmospheric pressure the lower the velocity, and the corresponding value of W. The results so obtained are plotted on a diagram as in Fig. 1, in which vertical distances represent pressures in pounds per square inch, and horizontal distances represent diameters of the contracting pipe. The curves then show the relation between the diameters of the pipe at various sections thereof, and the pressures atthose sections for each of the three selected speeds of flow of the air, which correspond a proximately to the maximum speed (when the engine is runnin at top speed) the normal speed, and the lowest ordmary working speed respectively. The lowest curve in Flg. 1 corresponds with the maximum speed and the highest curve corresponds with the lowest speed. The initial pressures 72, have been assumed as being.

13.7, 14 and 14.3 pounds per square inch for the maximum, normal and lowest speeds respectively, as the result of experiments, and the pipe has been chosen with a largest diameter of one inch. Having drawn these curves a pair of straight edges, designated by the lines K L and M N, are moved about in a vertical position over the curves until a position is foundfor the lines in which a certain relation holds good; that is to say, when horizontal lines are drawn from the points where the line M N cuts the threecut the base line, and these are the desired pressure ratios because they are proportional to the square of the differences in speeds of flow of the air-through the pipe. If these pressure differences are used .in injecting the spirit at the oint of narrower section (corresponding with'the position of M N) the amount of spirit injected will be proportional to the air flowing, because the amount of spirit which will flow through the orifice is proportional to the square root of the pressure under which it is forced to flow. The actual ratios of A B: CD: E F are nearly 1.15: 4:92 in the diagram; this is a desirable departure from the exact proportions stated above because it will result in a richer mixture being made at low speeds (as is desired for starting purposes for instance) and a slightly richer mixture at very high speeds when maximum power is to be developed. The strength of the mixture is nearly constant for a wide range'of intermediate speeds. Thepoints where KL and M N cut the base line correspond with diameters of the pipe of 0.88 and 0.98 ofv an inch respectively. The smallest diameter at the throat of the pipe may be about 0.78 of an inch without disturbing the stream-line flow, if the angle of taper is small. The diameter of the orifice through which the spirit is fed into the pipe is estimated from known data to be 1.375 millimeters to obtain In the drawings, a carbureter is illustrated, designed as above explained.

tle valve which is fitted into the pipe 6- in the lower part thereof and is preferably formed to the same taper, as shown. it is a short cylinder or ferrule which may be fitted on the top of the carbureter pipe b, and which may be cylindrical in bore, the object of this ferrule being to secure streamline flow in the air before it gets into the pipe 72 itself. The pipe I) is one inch in diameter at the top where the line 70 is marked -in diameter at the middle portion marked n whichmay be cylindrical. From this point onward down the pipe the section increases again until it may be 1 inch at the bottom end 0. The pipe need not necessarily be truly conical in the parts of varying section but it is shown so for convenience. Any suitable form of throttle may be used, butthe plug valve 9 is indicated as a convenient form of valve, a conical seating being turned out within the lower part of the pipe 6, and the plug 9 of conical form which fits in the seating being bored with the tapering passage shown. The plug valve is held in place by a stud and nut 72, and is adapted to be turned by means of a handle (which is partially indicated) for the purpose of partly closing the passage in the pipe I) and so reducing the flow of air therethrough. The irregularity in the flow caused by the plug 9 in the-lower part of the pipe will notappreciably disturb the stream-line flow in the upper part above the throat n so that the the flanges of the parts 0 and d, (see Figs.

8 and 9) the said diaphragm being clrcumferentially corrugated so that the diaphragm will move laterally owing to differences of pressure at the two sides thereofL. At the center of the diaphragm a boss 8 is secured, this boss being formedfor instance as a nut and a bolt screwing together to clamp the diaphragm between them. On one side of the boss 8 is arranged a rod t with a tapered point acting as a needle valve in a seating a. This rod t iS=--arranged so as to follow the movement of'the boss 8. It may be at tached to the said boss in such a manner as not to interfere with the free movement of the diaphragm but it is preferably mounted so as to be pressed by a spring-against a tapering point on the boss 8. In the arrangement illustrated in the drawings a small collar is formed on the end of the rod t adjacent to the boss .9 and a groove is formed infront of this collar. In this groove engages the forked end of a strip spring t which is mounted on the member 0 and presses against the collar on the rod t so as to cause this rod to follow the movement of the'diaphra-gm s away from the seating u. The pipe conveying the liquid fuel to the carbureter is shown at 0 opening into the valve seating u. From the seating u a branch passage w leads into the chamber in the member c, and there is a suitable cock :0 1n the branch passage, this cock being normally set to close the passage and being opened only for instance when it is required to fill the carbureter chamber in starting working therewith or after emptying the same- At the top of the diaphagm 1' holes are formed to allow the air pressure to be equalized at both sides of the diaphragm and-also to allow for the flow of the liquid fuel at a certain level. In Fig. 9 two holes 11 are shown for the flow of the liquid, and another hole 10 at a higher level which will insure the equalization of the air pressures. A duct 3/ (referred to hereinbefore as the air pressure duct) formed in the projecting side portion of the carbureter pipe leads from the top of the diaphragm chamber at the right-hand side thereof as seen in Fig. 2 up to an orifice in the carbureter pipe I) at the line Z where the diameter in the pipe is .98 of an inch. Another passage 2 leads from a point near the bottom ofthe diaphragm chamber at the right-hand Side thereof as seen in dotted lines in Fig. 2 up to the interior of the projection f, in which is a ferrule 2' fitted in a bore in the projection f, and held against a seating at the inner end thereof by means of a screw plug 12. The

ferrule 71 has a central orifice, which is on the line m as seen in Fig. 2, and a hole at 13 communicating with the passage 2 so that the liquid fuel forced out from the diaphragm chamber 0" through the passage .2 can reach the interior of the ferrule 2', and can enter the pipe 6 from the small orifice at the inner end of the said ferrule.

The working of this carbureter will now be evident with very little further explanation. Assuming the diaphragm chamber to be empty at both sides of the diaphragm the plug valve 00 will be turned to admit a little liquid fuel into the chamber at the left-hand side of the diaphragm (Fig. 2) and then as the chamber fills the diaphragm 7' will become pressed back causing the needle 'the right-hand side to approximately the level indicated in Fig. 2, and the parts are at the right-hand side falls again, thu upsetting the balance of pressure and causing the needle valve t to open. The level of the liquid'at the rlght-hand or outlet side of the diaphragm will not'in practice vary greatly because directly thelevel begins to sink the valve will open and more liquid will be admitted which. will overflow to the outlet side of the diaphragm. The device then serves to maintain the liquid at an approximately constant level in the chamber communicating with the fuel inlet orifice in the member '5. This orifice is a little way above the level of the liquid so that there is no risk that the liquid will flood the passage leading to the orifice, and escape. When the engine is drawing in a charge however there will be the differences of air pressure produced between the opening of the air pressure duct y and the fuel orifice in the member 71, and the increased pressure on the surface of the liquid in the diaphragm chamber will cause the liquid to be ejected through the passage 2 and ferrule a into the carbureter pipe I), the amount of liquid injected varying with the amount of air flowing through the pipe in the manner already explained; The little difference in pressure due to the fact that the orifice of the ferrule 71 is above the level of the liquid in the diaphragm .chamber will make no appreciable difference to the amount of the liquid fuel injected through the said orifice. The variations in the air pressure in the diaphragm chamber at different speeds of flow of the air through the carburetor pipe will be communicated equally to both sides of the diaphragm 1- so that they will have no effect on the said diaphragm, and will not cause thevalve t to open and close. The opening of the said valve will depend therefore solely upon the falling of the level of the liquid at the outlet side of the diaphragm. The throttle valve 9 will be used in the well known way to reduce the supply of carbure'ted air when the engine is running fast, and when the full power is not required, and then of course the amount of air passing through the pipe will be reduced, but-the carbureter will always work under normal circumstances within the ranges of speed of air for which it was designed.

The construction of the carbureter can of course be varied considerably but the arrangement shown in Figs. 2, 3 and 4 indicates the experimental form -of the carbureter. The carbureter pipe I) need not necessarily be vertical although that will be the most convenient position of the pipe for many types of engines. The pipe 6 may be horizontal if preferred or in any other po- .sition, and of course its section will be the same for working with the same engine, no matter what its position. In a vertical pipe the parts may be suitably transposed to allow the air to flow in an upward instead of a downward direction.

Fig. 5 shows a section through a horizontal carbureter pipe b taken on the line at where the fuel inlet orifice is. The parts 0 and d including the diaphragm chamber and inlet valve may be the same as in the construction already described; the ferrule '5 in which is formed the fuel inlet orifice is shown as being arranged vertically and opening into the carbureter pipe at the lower end of the vertical diameter thereof. This view will'require no further explanation and it will be obvious that the carbureter will work in this case in precisely the same manner as the carbureter shown in Figs. 2, 3, and 4. The air pressure duct s not indicated in Fig. 5 but of course it communicates with the carbureter pipe at a point of larger section and leads into the diaphragm chamber above the level of the liquid just as in Fig. 2.

Fig. 6 shows a type of fuel inlet orifice as applied to a horizontal'carbureter pipe, this orifice having a crew plug 15 formed with a conical head 16 adjustable in the said orifice 17 in the pipe I). The object of this construction is to enable the fuel inlet orifice to be adjusted when required. A look nut 18 secures the plug 15 in the position in which it is set.

In Fig. 7 a tapered plug valve 19 is shown forming an adjustable fuel inlet valve. The tapered plug 19 i held in place register wholly or partially with the orifice 21 leading into the carbureter pipe I). In this way the size of the orifice can be adjusted. Of course it is not intended that the adjustable valve should be altered in its setting during normal working but it would be altered if the feed of fuel was found to be too low or too high, and then the automatic \variations in the fuel supply with difierent amounts of air flowing through the carbureter pipe would insure the correct proportionality between the fuel and air at the different speeds of the en 'ne. 7

Various modifications in t e apparatus can be made without departing from the scope of the invention. For instance the diaphragm feed device may be replaced by any known equivalent device for maintaining the spirit at a constant level in the feed chamber. Further, any other arrangement for filling the said chamber with spirit at nearer to or even it may be at the throat nof the pipe when designed for certain amounts of air and ranges of speeds as hereinbefore explained. It is preferable however, to have a throat in the pipe beyond the spirit inlet orifice as shown, so that there will be a reduction of pressure with consequent further expansion in passing through the throat n,.which will assist in the vaporization of the spirit. The throat also protects the carbureter against the efiects of resurgence due to sudden pressure changes in the pipe leading to the engine. lhe direction of flow ofthe air through the carbureter pipe might be reversed, as the pressure differences would still be practically the same for the same speeds of flow. .The

pipe need not vary uniformly in section, but

anydesired form of pipe of varying section may be used, provided that there is no sudden change of section such as would be likely to produce eddies in the air.

The invention is evidently applicable for mixing any readily vapori zable liquid with a gas, and the word air may be read throughout as covering also other gases than air, while spirit or liquid fuel covers any readily vaporizable liquid to be mixed with the gas. Similarly the word carbureter may be read as including a mixing apparatus of thetype described, for. a gas and a vaporizable liquid, used for any suit; able purpose.

We claim as our inventions-- 1. In a carbureting apparatus, the combi- -nation of a pipe of gradually varying section with two openings therem at points of different section, the said sections being of areas such that the fluid pressure differences between said openings caused by 'the flow of air through the pipe at varying speeds and the corresponding varying pressures at,

the two openings are substantially proportional to the square of the quantity of air flowing at the various speeds, connecting passages between said openings and means for supplying spirit to one of the passages under a gaseous pressure head determined by the other passage.

2. In a carbureting apparatus, the combination of a pipe of gradually varying section with two openings therein at points of different section, the said sections being of areas such that the fluid pressure differences between said openings caused by the flow of air through the pipe at varying speeds, and the corresponding varying pressures at the two openings are substantially proportional to the square of the quantity of air flowing at the various speeds, a chamber and means of supplying spirit thereto, a passage leading from the opening at the larger section of the pipe to the upper part of said chamber,

and another passage leading from below the level of the spirit in said chamber to the opening in the pipe at the smaller section thereof.

3. In a carbureting apparatus, the combination of a pipe of gradually varying section formed with an .intermediate throat whose free sectional area is more than sixty per cent. of the sectional area at the inlet of the pipe, said pipe having two apertures, one at a point of larger section and the other at a pointof smaller section, connect-ing passages between said apertures, and means for supplying spirit to one of said passages under a gaseous. pressure head determined by the other passage.

4. In a carbureting apparatus, the combination of a pipe of gradually varying section contracting from the inlet end to a throat whose free sectional area is more than sixty per cent. of the sectional area at the inlet, said pipe being formed with two apertures at points of diflerent sectional area, both at the side of the throat at which the inlet lies, connecting passages between said apertures, and means for supplying spirit to one of said passages under a gas eous pressure head determined by the other passage.

,, In witness whereof, we have hereunto signed our names this 22nd day of March 1912, in the presence of two subscribing witnesses.

. Witnesses to allthe signatures: ERNOLD SIMPSON MOSELEY, MALCOLM SMn-THURs'r.

Images